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Wasowicz TJ, Dąbkowska I, Kivimäki A, Richter R. Two-body dissociation of isoxazole following double photoionization - an experimental PEPIPICO and theoretical DFT and MP2 study. Phys Chem Chem Phys 2023; 25:31655-31666. [PMID: 37964643 DOI: 10.1039/d3cp03760f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2023]
Abstract
The dissociative double photoionization of isoxazole molecules has been investigated experimentally and theoretically. The experiment has been carried out in the 27.5-36 eV photon energy range using vacuum ultraviolet (VUV) synchrotron radiation excitation combined with ion time-of-flight (TOF) spectrometry and photoelectron-photoion-photoion coincidence (PEPIPICO) technique. Five well-resolved two-body dissociation channels have been identified in the isoxazole's coincidence maps, and their appearance energies have been determined. The coincidence yield curves of these dissociation channels have been obtained in the photon energy ranges from their appearance energies up to 36 eV. The double photoionization of isoxazole produces a C3H3NO2+ transient dication, which decomposes into fragments differing from previously reported photofragmentation products of isoxazole. We have found no evidence of pathways leading to the C3H2NO+, HCN+, C2H2O+, C3HN+, or C2H2+ fragments or their neutral counterparts that have been observed in previous neutral photodissociation and single photoionization studies. Instead, the dissociation of isoxazole after the ejection of two electrons is bond-selective and is governed by two reactions, HCO+ + H2CCN+ and H2CO+ + HCCN+, whose appearance energies are 28.6 (±0.3) and 29.4 (±0.3) eV, respectively. A third dissociation channel turns out to be a variant of the most intense channel (HCO+ + H2CCN+), where one of the fragment ions contains a heavy isotope. Two minor dissociation channels occurring at higher energies, CO+ + CH3CN+ and CN+ + H3CCO+, are also identified. The density functional and ab initio quantum chemical calculations have been performed to elucidate the dissociative charge-separating mechanisms and determine the energies of the observed photoproducts. The present work unravels hitherto unexplored photodissociation mechanisms of isoxazole and thus provides deeper insight into the photophysics of five-membered heterocyclic molecules containing two heteroatoms.
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Affiliation(s)
- Tomasz J Wasowicz
- Division of Complex Systems Spectroscopy, Institute of Physics and Computer Science, Gdansk University of Technology, ul. G. Narutowicza 11/12, 80-233 Gdansk, Poland.
| | - Iwona Dąbkowska
- Department of Analytical Chemistry, Faculty of Chemistry, University of Gdansk, ul. Wita Stwosza 63, 80-308 Gdansk, Poland
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Priya H, Paranjothy M. Collision Induced Dissociation of Deprotonated Isoxazole and 3-Methyl Isoxazole via Direct Chemical Dynamics Simulations. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:710-719. [PMID: 36951239 DOI: 10.1021/jasms.2c00366] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/18/2023]
Abstract
Isoxazoles are an important class of organic compounds widely employed in synthesis and drug design. Fragmentation chemistry of the parent isoxazole molecule and its substituents has been the subject of several experimental and theoretical investigations. Collision induced dissociation (CID) of isoxazole and its substituents has been studied experimentally under negative ion conditions. Based on the observed reaction products, dissociation patterns were proposed. In the present work, we studied the dissociation chemistry of deprotonated isoxazole and 3-methyl isoxazole using electronic structure theory calculations and direct chemical dynamics simulations. Various deprotonated isomers of these molecules were activated by collision with an Ar atom, and the ensuing fractionation patterns were studied using on-the-fly classical trajectory simulations at the density functional B3LYP/6-31+G* level of electronic structure theory. A variety of reaction products and pathways were observed, and it was found that a nonstatistical shattering mechanism dominates the CID dynamics of these molecules. Simulation results are compared with experiments, and detailed atomic level dissociation mechanisms are presented.
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Affiliation(s)
- Himani Priya
- Department of Chemistry, Indian Institute of Technology Jodhpur, Jodhpur, 342030 Rajasthan, India
| | - Manikandan Paranjothy
- Department of Chemistry, Indian Institute of Technology Jodhpur, Jodhpur, 342030 Rajasthan, India
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3
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Chitarra O, Pirali O, Spaniol JT, Hearne TS, Loison JC, Stanton JF, Martin-Drumel MA. Pure Rotational Spectroscopy of the CH 2CN Radical Extended to the Sub-Millimeter Wave Spectral Region. J Phys Chem A 2022; 126:7502-7513. [PMID: 36198131 DOI: 10.1021/acs.jpca.2c04399] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We present a thorough pure rotational investigation of the CH2CN radical in its ground vibrational state. Our measurements cover the millimeter and sub-millimeter wave spectral regions (79-860 GHz) using a W-band chirped-pulse instrument and a frequency multiplication chain-based spectrometer. The radical was produced in a flow cell at room temperature by H abstraction from acetonitrile using atomic fluorine. The newly recorded transitions of CH2CN (involving N″ and Ka″ up to 42 and 8, respectively) were combined with the literature data, leading to a refinement of the spectroscopic parameters of the species using a Watson S-reduced Hamiltonian. In particular, the A rotational constant and K-dependent parameters are significantly better determined than in previous studies. The present model, which reproduces all experimental transitions to their experimental accuracy, allows for confident searches for the radical in cold to warm environments of the interstellar medium.
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Affiliation(s)
- Olivia Chitarra
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405Orsay, France
| | - Olivier Pirali
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405Orsay, France
| | - Jean-Thibaut Spaniol
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405Orsay, France
| | - Thomas S Hearne
- Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405Orsay, France
| | | | - John F Stanton
- Quantum Theory Project, Department of Chemistry, University of Florida, Gainesville32611, Florida, United States
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Dias N, Gurusinghe RM, Suits AG. Multichannel Radical-Radical Reaction Dynamics of NO + Propargyl Probed by Broadband Rotational Spectroscopy. J Phys Chem A 2022; 126:5354-5362. [PMID: 35938878 DOI: 10.1021/acs.jpca.2c01629] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Chirped-pulse rotational spectroscopy in a quasi-uniform flow has been used to investigate the reaction dynamics of a multichannel radical-radical reaction of relevance to planetary atmospheres and combustion. In this work, the NO + propargyl (C3H3) reaction was found to yield six product channels containing eight detected species. These products and their branching fractions (%), are as follows: HCN (50), HCNO (18), CH2CN (12), CH3CN (7.4), HC3N (6.2), HNC (2.3), CH2CO (1.3), HCO (1.8). The results are discussed in light of previous unimolecular photodissociation studies of isoxazole and prior potential energy surface calculations of the NO + C3H3 system. The results also show that the product branching is strongly influenced by the excess energy of the reactant radicals. The implications of the title reaction to the planetary atmospheres, particularly to Titan, are discussed.
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Affiliation(s)
- Nureshan Dias
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211 United States
| | - Ranil M Gurusinghe
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211 United States
| | - Arthur G Suits
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211 United States
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Gurusinghe RM, Dias N, Mebel AM, Suits AG. Radical-Radical Reaction Dynamics Probed Using Millimeterwave Spectroscopy: Propargyl + NH 2/ND 2. J Phys Chem Lett 2022; 13:91-97. [PMID: 34958581 DOI: 10.1021/acs.jpclett.1c03813] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
We apply chirped-pulse uniform flow millimeterwave (CPUF-mmW) spectroscopy to study the complex multichannel reaction dynamics in the reaction between the propargyl and amino radicals (C3H3 + NH2/ND2), a radical-radical reaction of importance in the gas-phase chemistry of astrochemical environments and combustion systems. The photolytically generated radicals are allowed to react in a well-characterized quasi-uniform supersonic flow, and mmW rotational spectroscopy (70-93 GHz) is used for simultaneous detection of the reaction products: HCN, HNC, HC3N, DCN, DNC, and DC3N, while spectral intensities of the measured pure-rotational lines allow product branching to be quantified. High-level electronic structure calculations were used for theoretical prediction of the reaction pathways and branching. Experimentally deduced product branching fractions were compared with the results from statistical simulations based on the RRKM theory. Product branching was found to be strongly dependent on the excess internal energy of the C3H3 and NH2/ND2 reactants.
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Affiliation(s)
- Ranil M Gurusinghe
- Department of Chemistry, University of Missouri, Columbia, Missouri 65201, United States
| | - Nureshan Dias
- Department of Chemistry, University of Missouri, Columbia, Missouri 65201, United States
| | - Alexander M Mebel
- Department of Chemistry and Biochemistry, Florida International University, Miami, Florida 33199, United States
| | - Arthur G Suits
- Department of Chemistry, University of Missouri, Columbia, Missouri 65201, United States
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Gurusinghe RM, Dias N, Krueger R, Suits AG. Uniform supersonic flow sampling for detection by chirped-pulse rotational spectroscopy. J Chem Phys 2022; 156:014202. [PMID: 34998338 DOI: 10.1063/5.0073527] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Chirped-pulse Fourier transform microwave (CP-FTMW) spectroscopy is a powerful near-universal detection method finding application in many areas. We have previously coupled it with supersonic flows (CPUF) to obtain product branching in reaction and photodissociation. Because chirped-pulse microwave detection requires monitoring the free induction decay on the timescale of microseconds, it cannot be employed with good sensitivity at the high densities achieved in some uniform supersonic flows. For application to low-temperature kinetics studies, a truly uniform flow is required to obtain reliable rate measurements and enjoy all the advantages that CP-FTMW has to offer. To this end, we present a new setup that combines sampling of uniform supersonic flows using an airfoil-shaped sampling device with chirped-pulse mmW detection. Density and temperature variations in the airfoil-sampled uniform flow were revealed using time-dependent rotational spectroscopy of pyridine and vinyl cyanide photoproducts, highlighting the use of UV photodissociation as a sensitive diagnostic tool for uniform flows. The performance of the new airfoil-equipped CPUF rotational spectrometer was validated using kinetics measurements of the CN + C2H6 reaction at 50 K with detection of the HCN product. Issues relating to product detection by rotational spectroscopy and airfoil sampling are discussed. We show that airfoil sampling enables direct measurements of low temperature reaction kinetics on a microsecond timescale, while rotational spectroscopic detection enables highly specific simultaneous detection of reactants and products.
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Affiliation(s)
- Ranil M Gurusinghe
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Nureshan Dias
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Ritter Krueger
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
| | - Arthur G Suits
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA
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Gurusinghe RM, Dias N, Broderick BM. Buffer gas cooling for sensitive rotational spectroscopy of ice chemistry: A proposal. Chem Phys Lett 2021. [DOI: 10.1016/j.cplett.2020.138125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Hearne TS, Abdelkader Khedaoui O, Hays BM, Guillaume T, Sims IR. A novel Ka-band chirped-pulse spectrometer used in the determination of pressure broadening coefficients of astrochemical molecules. J Chem Phys 2020; 153:084201. [PMID: 32872880 DOI: 10.1063/5.0017978] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A novel chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer has been constructed to cover the Ka-band (26.5 GHz-40 GHz) for use in the CRESUCHIRP project, which aims to study the branching ratios of reactions at low temperatures using the chirped-pulse in uniform flow technique. The design takes advantage of recent developments in radio-frequency components, notably, high-frequency, high-power solid-state amplifiers. The spectrometer had a flatness of 5.5 dB across the spectral range, produced harmonic signals below -20 dBc, and the recorded signal scaled well to 6 × 106 averages. The new spectrometer was used to determine pressure broadening coefficients with a helium collider at room temperature for three molecules relevant to astrochemistry, applying the Voigt function to fit the magnitude of the Fourier-transformed data in the frequency domain. The pressure broadening coefficient for carbonyl sulfide was determined to be (2.45 ± 0.02) MHz mbar-1 at room temperature, which agreed well with previous measurements. Pressure broadening coefficients were also determined for multiple transitions of vinyl cyanide and benzonitrile. Additionally, the spectrometer was coupled with a cold, uniform flow from a Laval nozzle. The spectrum of vinyl cyanide was recorded in the flow, and its rotational temperature was determined to be (24 ± 11) K. This temperature agreed with a prediction of the composite temperature of the system through simulations of the experimental environment coupled with calculations of the solution to the optical Bloch equations. These results pave the way for future quantitative studies in low-temperature and high-pressure environments using CP-FTMW spectroscopy.
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Affiliation(s)
- Thomas S Hearne
- Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
| | | | - Brian M Hays
- Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
| | - Théo Guillaume
- Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
| | - Ian R Sims
- Univ. Rennes, CNRS, IPR (Institut de Physique de Rennes) - UMR 6251, F-35000 Rennes, France
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Geng T, Ehrmaier J, Schalk O, Richings GW, Hansson T, Worth G, Thomas RD. Time-Resolved Photoelectron Spectroscopy Studies of Isoxazole and Oxazole. J Phys Chem A 2020; 124:3984-3992. [PMID: 32242664 PMCID: PMC7304896 DOI: 10.1021/acs.jpca.9b11788] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
The
excited state relaxation pathways of isoxazole and oxazole
upon excitation with UV-light were investigated by nonadiabatic ab
initio dynamics simulations and time-resolved photoelectron spectroscopy.
Excitation of the bright ππ*-state of isoxazole predominantly
leads to ring-opening dynamics. Both the initially excited ππ*-state
and the dissociative πσ*-state offer a combined barrier-free
reaction pathway, such that ring-opening, defined as a distance of
more than 2 Å between two neighboring atoms, occurs within 45
fs. For oxazole, in contrast, the excited state dynamics is about
twice as slow (85 fs) and the quantum yield for ring-opening is lower.
This is caused by a small barrier between the ππ*-state
and the πσ*-state along the reaction path, which suppresses
direct ring-opening. Theoretical findings are consistent with the
measured time-resolved photoelectron spectra, confirming the timescales
and the quantum yields for the ring-opening channel. The results indicate
that a combination of time-resolved photoelectron spectroscopy and
excited state dynamics simulations can explain the dominant reaction
pathways for this class of molecules. As a general rule, we suggest
that the antibonding σ*-orbital located between the oxygen atom
and a neighboring atom of a five-membered heterocyclic system provides
a driving force for ring-opening reactions, which is modified by the
presence and position of additional nitrogen atoms.
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Affiliation(s)
- Ting Geng
- Department of Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
| | - Johannes Ehrmaier
- Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748 Garching, Germany
| | - Oliver Schalk
- Department of Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden.,Department of Chemistry, University of Copenhagen, Universitetsparken 5, DK-2100 Copenhagen, Denmark
| | - Gareth W Richings
- Department of Chemistry and Centre for Scientific Computing, University of Warwick, CV4 7AL Coventry, U.K
| | - Tony Hansson
- Department of Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
| | - Graham Worth
- Department of Chemistry, University College London, 20 Gordon Street, WC1H 0AJ London, U.K
| | - Richard D Thomas
- Department of Physics, AlbaNova University Centre, Stockholm University, Roslagstullsbacken 21, 106 91 Stockholm, Sweden
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